Embersmith

The artifact-matters payoff that turns every cheap trinket you cast into a point of reach. The 2/1 body is incidental; the engine is the repeatable -for-one-damage tax it levies on your own artifact-heavy turns, which means the card scales with how cheaply you can spew permanents onto the stack. Drop a fistful of zero-cost and one-cost artifacts in a turn and it stops reading like a creature and starts reading like a slow burn, picking off X/1 utility creatures one trigger at a time or chipping points at a face. The constraint that holds it back is the second on every ping: the damage is never free, so the card rewards a deck that generates surplus mana alongside its artifact density rather than one merely flush with cheap artifacts. That dual demand (you need both the spells to trigger it and the mana to fire it) is what files it down from a menace to a synergy piece, dependent on a critical mass the surrounding deck has to supply. The trigger keys off the cast rather than a tap or an enter-the-battlefield event, which front-loads the damage onto the stack the moment you commit the artifact spell, no separate activation step required; whether you ever get to do this on an opponent's turn depends entirely on giving your artifacts flash, since by default they only deploy at sorcery speed.